In addition to sullying their surroundings, rats bite and scratch when they feel threatened. Since they transmit several serious diseases, rat bites and scratches leave humans susceptible to any number of viruses, including rat-bite fever, the plague, and lymphocytic choriomeningitis (LCMV). The rodents may also carry smaller pests like fleas. Finally, as accomplished burrowers, rats damage building foundations and sidewalks and gnaw on a variety of objects, leaving behind unseemly teeth marks.